Heretofore, contact device has been provided in which a movable shaft is moved in the axial direction due to turning on/off energization of an electromagnet block, and movable contacts are brought into contact with and separated from fixed contacts, in conjunction with movement of the movable shaft. The contact device includes a pressing spring that gives biasing force to the movable contacts toward the fixed contacts in order to secure pressing force between the contacts when the movable contacts are in contact with the fixed contacts (closed state).
In recent years, since downsizing of the contact device is desired, downsizing of individual parts of the contact device has been in progress, and the pressing spring has been downsized as well. Here, a coil spring is generally used as the pressing spring, and the coil spring is arranged in a state of being contracted by a predetermined length from the natural length. Then, when the pressing spring is downsized, since the pressing force working between the movable contacts and the fixed contacts decreases, a pressing spring having a high spring constant has been used in order to suppress reduction of the pressing force, while downsizing the pressing spring. The larger the spring constant of the pressing spring is, the larger the increase/decrease of the biasing force becomes relative to a change of an extension and contraction amount of the pressing spring.
However, when the contraction amount of the pressing spring (initial contraction amount) when the movable contacts are separated from the fixed contacts (open state) differs in each contact device, variability occurs in open state pressing force (initial pressing force) among the contact devices. Thus, there may be a contact device in which the pressing force in the closed state is less than a predetermined pressing force. Therefore, taking into consideration the variability of the pressing force among the contact devices, an electromagnet block that can generate stronger electromagnetic force needs to be provided in each contact device. Note that the initial pressing force refers to pressing force of the pressing spring against the movable contact maker when the movable contact is separated from the fixed contact (open state).
However, when the size of the electromagnet block is increased, the size of the contact device increases, thus making downsizing of the contact device difficult. Accordingly, the variability of spring loads needs to be reduced by making the initial contraction amounts of the pressing springs the same in the contact devices.
In view of this, a contact device that is capable of adjusting the spring load has been proposed (refer to JP 2012-48907A, for example). The contact device includes a configuration in which the movable contact maker and the pressing spring are sandwiched by an adjustment plate and a holding member, and the adjustment plate is fixed to the holding member by welding at a position at which the pressing force of the pressing spring is a predetermined value. This conventional contact device will be described with reference to FIGS. 10 and 11. Note that description will be given using upper, lower, right, and left in FIG. 10 as references, and the direction orthogonal to the upper and lower, and right and left directions is a front and rear direction.
The conventional contact device includes, as shown in FIGS. 10 and 11, fixed terminals 33 respectively including fixed contacts 32, a movable contact maker 35 including movable contacts 34, a pressing spring 36, an adjustment plate 61, a holding member 5A, a movable shaft 8, and an electromagnet block 2.
Each of the fixed terminals 33 is formed in a substantially columnar shape of a conductive material such as copper, and has the fixed contact 32 fixed to a lower end. Note that the fixed contact 32 may be formed integrally with the fixed terminal 33.
The movable contact maker 35 is formed in a substantially rectangular plate-like shape, and the movable contacts 34 are fixed to respective right and left end sides of an upper face thereof, the movable contacts 34 being arranged at positions opposing the respective fixed contacts 32 with a predetermined space. Also, a positioning protrusion 35a having a substantially disk-like shape is formed at approximately the center of the lower face of the movable contact maker 35.
The pressing spring 36 is constituted of a coil spring, and is arranged in a state in which an axial direction thereof is in the up and down direction, and is positioned relative to the movable contact maker 35 by the positioning protrusion 35a being fitted into an inner diameter portion on an upper end side.
The holding member 5A includes a bottom plate 51A, and a pair of side plates 52A that extend upward respectively from the front and rear edges of the bottom plate 51A and oppose each other in the front and rear direction, and thus has a substantially U-shaped cross section.
The bottom plate 51A is formed in a substantially rectangular plate-like shape, and an upper face thereof is in contact with a lower end of the pressing spring 36 and opposes the lower face of the movable contact maker 35 via the pressing spring 36. That is, the pressing spring 36 is sandwiched between the bottom plate 51A and the movable contact maker 35 in the up and down direction.
Each of the pair of side plates 52A is formed in a substantially rectangular plate-like shape. A front end of the movable contact maker 35 is in sliding contact with an inner face (rear face) of the front side plate 52A, and a rear end of the movable contact maker 35 is in sliding contact with an inner face (front face) of the rear side plate 52A.
The movable shaft 8 is formed in a substantially bar-like shape elongated in the up and down direction, the electromagnet block 2 is connected to a lower end, and an upper end is connected to the lower face of the bottom plate 51A at approximately the center thereof.
The adjustment plate 61 is formed in a substantially rectangular plate-like shape, is inserted between the pair of side plates 52A from above, and is mounted on an upper face of the movable contact maker 35 at approximately the center thereof. Then, by pressing the adjustment plate 61 downward, the adjustment plate 61 and the movable contact maker 35 move downward against biasing force of the pressing spring 36, and the pressing force of the pressing spring 36 against the movable contact maker 35 increases. Note that, hereinafter, the pressing force of the pressing spring 36 against the movable contact maker 35, when the movable contact 34 is separated from the fixed contact 32 (open state), is referred to as initial pressing force. Here, when the adjustment plate 61 is moved further downward, the initial pressing force can be increased more, and when the adjustment plate 61 is moved upward, the initial pressing force can be reduced.
Also, the front and rear ends of the adjustment plate 61 are respectively fixed to the pair of side plates 52A, at a position at which the initial pressing force is a predetermined value, by welding, for example. Accordingly, the initial pressing force can be adjusted easily.
Then, the movable contact maker 35 is pressed upward by the pressing spring 36, and the upper face thereof comes into contact with the adjustment plate 61 so that movement toward the fixed contacts 32 is restricted.
Resistance welding is generally known as a method of welding metals together. Resistance welding is a welding method in which a large electric current is applied to a welding portion, and the welding portion is welded by heating due to Joule heat generated at the contact point and by pressure applied simultaneously, and the welding time can be shortened.
However, in the conventional contact device, since the holding member 5A is formed to have a substantially U-shaped cross section, the side plates 52A, which is a pair, are brought into conduction via the bottom plate 51A. As a result, since the electric current that flows between each side plate 52A and the adjustment plate 61 decreases, it has been difficult to perform resistance welding between the holding member 5A (side plates 52A) and the adjustment plate 61.